Before that, lead levels at test sites had touched the maximum acceptable 15-ppb threshold just once, in 2002. The city has monitored lead levels in some buildings since 1992, when the EPA passed regulations that required municipalities to conduct water tests.

The 2010 results meant the water district, which serves customers in Bangor, Eddington, Clifton, Orrington, Hampden, Veazie and Hermon, had to begin a public education campaign, review its water-treatment processes, and implement a ramped-up testing schedule.

That campaign and testing continue, and are showing promising results, according to Dina Page, water quality manager at the district.

Page said the district found that the lead isn’t coming from Bangor’s water supply or the utility’s distribution system, but rather internal plumbing components in individual properties.

When acidic water sits in lead pipes and plumbing joined by lead solder for more than six hours, the lead can leach into the water. Buildings with plumbing installed between 1982 and 1986 are especially vulnerable because the lead components were phased out in 1986 and water pipes installed before 1982 are likely to have developed an inner coating of mineral deposits that helps prevent lead from leaching into the water. The tests are meant to monitor the worst-case situations, where the test water is allowed to sit in pipes for six to 10 hours while leaching occurs.

The Bangor Water District has been testing 60 high-risk residences and businesses on a regular basis, and met the threshold of 90 percent of properties falling under 15 ppb in the most recent round of testing, according to Page. Some of the homes with the highest results saw a 50 percent reduction in their lead leaching levels.

Page said the water district has been tinkering with its water chemistry this year and has reduced its acidity to make it less corrosive and reduce the amount of lead that leaches from pipes.

Exposure to lead can cause lowered intelligence, neurological problems and brain and kidney dysfunction in adults and children. Pregnant women, infants and young children are at the greatest risk.

To decrease the likelihood of lead leaching into drinking water, residents may run cold water through their taps for two or three minutes each morning before drinking or cooking with it. That allows the water that has set in the pipes overnight to leave the system and allows fresh water to flow in.

Using hot water for flushing or speeding up the process of boiling water can cause lead to dissolve into the water.

“Time and temperature are really this issues,” Page said.

Boiling water does not remove lead.

Page said regular testing will continue, and that if the district continues to meet EPA requirements, it will be able to scale back the frequency of its testing from once every six months to once per year.